// Copyright (c) 2017 Ma Weiwei, Max Riveiro
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package socket

import (
	"bufio"
	"os"
	"strconv"
	"strings"

	"golang.org/x/sys/unix"
)

func maxListenerBacklog() int {
	fd, err := os.Open("/proc/sys/net/core/somaxconn")
	if err != nil {
		return unix.SOMAXCONN
	}
	defer fd.Close()

	rd := bufio.NewReader(fd)
	line, err := rd.ReadString('\n')
	if err != nil {
		return unix.SOMAXCONN
	}

	f := strings.Fields(line)
	if len(f) < 1 {
		return unix.SOMAXCONN
	}

	n, err := strconv.Atoi(f[0])
	if err != nil || n == 0 {
		return unix.SOMAXCONN
	}

	// Linux stores the backlog in a uint16.
	// Truncate number to avoid wrapping.
	// See issue 5030.
	if n > 1<<16-1 {
		n = 1<<16 - 1
	}

	return n
}
